Piston lubrication for a free piston engine

Abstract

A free piston engine is configured with a pair of opposed engine cylinders located on opposite sides of a fluid pumping assembly. An inner piston assembly includes a pair of inner pistons, one each operatively located in a respective one of the engine cylinders, with a push rod connected between the inner pistons. The push rod extends through an inner pumping chamber in the fluid pumping assembly and forms a fluid plunger within this chamber. An outer piston assembly includes a pair of pistons, one each operatively located in a respective one of the engine cylinders, with at least one pull rod connected between the outer pistons. The pull rod extends through an outer pumping chamber in the fluid pumping assembly and forms a fluid plunger within this chamber. The movement of the inner and outer piston assemblies during engine operation will cause the fluid plungers to pump fluid from a low pressure container into a high pressure chamber as a means of storing the energy output from the engine. Alternatively, the piston assemblies may drive a linear alternator. Located adjacent to at least one of the pistons are oil holes, with an oil mist annulus supplying oil mist therethrough. The oil in the oil mist will lubricate the engine cylinder wall while minimizing the oil consumption of the engine.

1. A free piston engine comprising:
 an energy generation and control assembly having a first side; 
 a first combustion cylinder assembly located adjacent to the first side of the energy generation and control assembly and including a first cylinder liner that defines a generally cylindrical first engine cylinder, with the first cylinder liner including a plurality of circumferentially spaced oil mist holes extending therethrough; 
 a piston assembly having a first piston located and telescopically slidable within the first engine cylinder and having an outer cylindrical surface adjacent to the plurality of oil mist holes, and a first rod mounted to the first piston and operatively engaging the energy generation and control assembly, wherein the piston assembly is an outer piston assembly, with the first piston having a piston head that faces the energy generation and control assembly and having a rear end; 
 a first scavenge pump engaged with the first combustion cylinder having a first scavenge pump housing, which defines an air inlet, an air outlet and includes a wall that defines a main pumping chamber selectively connectable to the air inlet and the air outlet, and with the main pumping chamber telescopically receiving the rear end of the first piston therein such that the rear end of the first piston seals against the wall of the main pumping chamber and is actuable to create an air pumping action in the main pumping chamber; and 
 an oil mister, adapted to mix oil with air to form an oil mist, and having an oil mist outlet in fluid communication with the plurality of oil mist holes. 
 
   
   
     2. The free piston engine of  claim 1  wherein:
 the energy generation and control assembly further includes a second side in opposed relation to the first side; 
 the free piston engine further includes a second combustion cylinder assembly located adjacent to the second side of the energy generation and control assembly and including a second cylinder liner that defines a generally cylindrical second engine cylinder, with the second cylinder liner including a plurality of circumferentially spaced oil mist holes extending therethrough and in fluid communication with the oil mist outlet of the oil mister; and 
 the piston assembly has a second piston located and telescopically slidable within the second engine cylinder and having an outer cylindrical surface adjacent to the plurality of oil mist holes, and with the second piston mounted to the first rod. 
 
   
   
     3. The free piston engine of  claim 2  wherein the first combustion cylinder assembly includes a first cylinder jacket that surrounds a portion of the first cylinder liner and defines a first oil mist annulus located radially outward of and adjacent to the plurality of oil mist holes, and with the first oil mist annulus including an oil mist inlet that is in fluid communication with the oil mist outlet of the oil mister; and wherein the second combustion cylinder assembly includes a second cylinder jacket that surrounds a portion of the second cylinder liner and defines a second oil mist annulus located radially outward of and adjacent to the plurality of oil mist holes in the second cylinder liner, and with the second oil mist annulus including a second oil mist inlet that is in fluid communication with the oil mist outlet of the oil mister. 
   
   
     4. The free piston engine of  claim 3  wherein the first and second oil mist annulus each include an oil mist outlet that is in fluid communication with an inlet to the oil mister. 
   
   
     5. The free piston engine of  claim 4  wherein the piston assembly is an outer piston assembly, with the first piston having a first piston head that faces the energy generation and control assembly and the second piston having a second piston head that faces the energy generation and control assembly. 
   
   
     6. The free piston engine of  claim 5  further including an inner piston assembly having a first inner piston located and telescopically slidable within the first engine cylinder and having a piston head that faces the piston head of the first piston, forming a first combustion chamber therebetween, a second inner piston located and telescopically slidable within the second engine cylinder and having a piston head that faces the piston head of the second piston, forming a second combustion chamber therebetween, and a push rod connected between the first and second inner pistons and including a middle portion that extends through and operatively engages the energy generation and control assembly. 
   
   
     7. The free piston engine of  claim 1  wherein the first combustion cylinder assembly includes a first cylinder jacket that surrounds a portion of the first cylinder liner and defines a first oil mist annulus located radially outward of and adjacent to the plurality of oil mist holes, and with the first oil mist annulus including an oil mist inlet that is in fluid communication with the oil mist outlet of the oil mister. 
   
   
     8. The free piston engine of  claim 7  wherein the first oil mist annulus includes an oil mist outlet that is in fluid communication with an inlet to the oil mister. 
   
   
     9. The free piston engine of  claim 8  further including an oil sump located between and in fluid communication with the oil mist outlet of the first oil mist annulus and the inlet to the oil mister. 
   
   
     10. The free piston engine of  claim 1  wherein the oil mister is adapted to selectively vary the amount of oil mist mixed with the air. 
   
   
     11. A free piston engine comprising:
 an energy generation and control assembly having a first side; 
 a first combustion cylinder assembly located adjacent to the first side of the energy generation and control assembly and including a first cylinder liner that defines a generally cylindrical first engine cylinder, with the first cylinder liner including a plurality of circumferentially spaced oil mist holes extending therethrough, and with the first combustion cylinder assembly also including a first cylinder jacket that surrounds a portion of the first cylinder liner and defines a first oil mist annulus located radially outward of and adjacent to the plurality of oil mist holes, with the first oil mist annulus including an oil mist inlet that is adapted to be in fluid communication with an outlet of an oil mister; and 
 a piston assembly having a first piston located and telescopically slidable within the first engine cylinder and having an outer cylindrical surface adjacent to the plurality of oil mist holes, and a first rod mounted to the first piston and operatively engaging the energy generation and control assembly. 
 
   
   
     12. The free piston engine of  claim 11  wherein the first oil mist annulus includes an oil mist outlet that is adapted to be in fluid communication with an inlet of the oil mister. 
   
   
     13. A free piston engine comprising:
 an energy generation and control assembly having a first side and a second side in opposed relation to the first side; 
 a first combustion cylinder assembly located adjacent to the first side of the energy generation and control assembly and including a first cylinder liner that defines a generally cylindrical first engine cylinder, with the first cylinder liner including a plurality of circumferentially spaced oil mist holes extending therethrough that are adapted to be in fluid communication with an outlet of an oil mister; 
 a second combustion cylinder assembly located adjacent to the second side of the energy generation and control assembly and including a second cylinder liner that defines a generally cylindrical second engine cylinder, with the second cylinder liner including a plurality of circumferentially spaced oil mist holes extending therethrough that are adapted to be in fluid communication with the outlet of the oil mister; and 
 a piston assembly having a first piston located and telescopically slidable within the first engine cylinder and having an outer cylindrical surface adjacent to the plurality of oil mist holes through the first cylinder liner, a second piston located and telescopically slidable within the second engine cylinder and having an outer cylindrical surface adjacent to the plurality of oil mist holes through the second cylinder liner, and a first rod mounted between the first piston and the second piston and operatively engaging the energy generation and control assembly. 
 
   
   
     14. The free piston engine of  claim 12  further including an oil sump adapted to be located between and in fluid communication with the oil mist outlet of the first oil mist annulus and an inlet to the oil mister. 
   
   
     15. The free piston engine of  claim 11  wherein:
 the energy generation and control assembly further includes a second side in opposed relation to the first side; 
 the free piston engine further includes a second combustion cylinder assembly located adjacent to the second side of the energy generation and control assembly and including a second cylinder liner that defines a generally cylindrical second engine cylinder, with the second cylinder liner including a plurality of circumferentially spaced oil mist holes extending therethrough and adapted to be in fluid communication with the outlet of the oil mister; and 
 the piston assembly has a second piston located and telescopically slidable within the second engine cylinder and having an outer cylindrical surface adjacent to the plurality of oil mist holes, and with the second piston mounted to the first rod. 
 
   
   
     16. The free piston engine of  claim 15  further including an inner piston assembly having a first inner piston located and telescopically slidable within the first engine cylinder and having a piston head that faces the first piston, forming a first combustion chamber therebetween, a second inner piston located and telescopically slidable within the second engine cylinder and having a piston head that faces the second piston, forming a second combustion chamber therebetween, and a push rod connected between the first and second inner pistons and including a middle portion that extends through and operatively engages the energy generation and control assembly. 
   
   
     17. The free piston engine of  claim 13  wherein the first combustion cylinder assembly includes a first cylinder jacket that surrounds a portion of the first cylinder liner and defines a first oil mist annulus located radially outward of and adjacent to the plurality of oil mist holes, and with the first oil mist annulus including an oil mist inlet that is adapted to be in fluid communication with the outlet of the oil mister; and wherein the second combustion cylinder assembly includes a second cylinder jacket that surrounds a portion of the second cylinder liner and defines a second oil mist annulus located radially outward of and adjacent to the plurality of oil mist holes in the second cylinder liner, and with the second oil mist annulus including a second oil mist inlet that is adapted to be in fluid communication with the outlet of the oil mister. 
   
   
     18. The free piston engine of  claim 17  wherein the first and second oil mist annulus each include an oil mist outlet that is adapted to be in fluid communication with an inlet to the oil mister. 
   
   
     19. The free piston engine of  claim 13  wherein the piston assembly is an outer piston assembly, with the first piston having a first piston head that faces the energy generation and control assembly and the second piston having a second piston head that faces the energy generation and control assembly. 
   
   
     20. The free piston engine of  claim 19  further including an inner piston assembly having a first inner piston located and telescopically slidable within the first engine cylinder and having a piston head that faces the piston head of the first piston, forming a first combustion chamber therebetween, a second inner piston located and telescopically slidable within the second engine cylinder and having a piston head that faces the piston head of the second piston, forming a second combustion chamber therebetween, and a push rod connected between the first and second inner pistons and including a middle portion that extends through and operatively engages the energy generation and control assembly.